Introduction

Objective of course BasicMacrovelocityconceptsModel Outline of the coursePrognosis

Drilling

Objective of course

Introduction

Objective:To understand the process of traveltime inversion and how to apply it bothefficiently and effectively.

1.1

Objective of course

Introduction

Travel Time Inversion

[t] x [V] [z]Have

Estimate

Abundant seismic xdata recorded in time

Need

Velocitymodel

Structural modelin depth

Objective of course

Introduction

Travel-Time InversionSeismicFieldData

Processing

MacroVelocityModel

WellData

TimeStructure

Travel-timeInversion

Structurein depth

The macro velocity model and form of travel time inversion

depend upon the structural complexity and amount of wellvelocity information available . . .1.2

Course Outline

Introduction

Velocity for T -Z Conversion

To depth convert seismic times we need: average velocity from datum to reflector or depth expressed in terms of travel-timeWe usually have: some checkshots (or VSP) sections of sonic logs some stacking or time migration velocitiesHow do we build the macro velocity model?

The Macrovelocity Model

Well velocitymodel

Seismic velocitymodel

These two views are not inconsistent, lower average velocity

at the edge of the basin, higher velocity in the centre.

Basic concepts

Introduction

Well DensityApproaches to depth mapping of the subsurface depend uponthe density of well control available.Categories are:Very dense less than 80 acre spacing (~300m)Dense80 240 acre spacing ( to 1 km)Moderate1 to 5 kmOccasional 5 to 25 kmSparseover 25 kmNoneAs the well density decreases we have to rely more on seismicvelocities1.12